Surface modification of substrates

ABSTRACT

The present invention is directed to a practically universal surface modification process and the materials thereby obtained. In general, the process includes initial epoxy modification of a substrate surface by attachment of an epoxy-containing polymer to the surface. Following attachment of the polymer, still-existing epoxy groups on the polymer may then cross-link the polymer to form a unified anchoring layer on the surface. Other epoxy groups in the anchoring layer, not utilized in forming the layer may be used to graft surface modifying materials to the surface. For instance, macromolecules, biomolecules, polymers, and polymerization initiators may be grafted to the surface via the anchoring layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit to U.S. Provisional Patent ApplicationSer. No. 60/446,004 filed Feb. 7, 2003.

BACKGROUND OF THE INVENTION

The surface characteristics of a substrate play a significant role inthe ability of the substrate to perform as desired. For example, in manyinstances, a substrate has the preferred characteristics, e.g. strength,malleability, permeability, thermal dynamic characteristics, etc., for adesired use, but the surface characteristics present operationaldifficulties under the conditions of use. For example, surfacecharacteristics of a substrate such as biocompatibility, wettability,reactivity, adhesion, resistance, colloidal stability, etc., may presentprocessability problems under the conditions of use. As such, a largefield of interest has developed in the modification of surfacecharacteristics of substrates.

A wide variety of processes have been developed in an effort to createand/or modify specific surface characteristics of both organic andinorganic materials. However, these processes tend to be very specificto both the substrate material and the specific surface modification.For example, laminating processes are often used for surfacemodification of textiles. Other processes, such as surface activationfollowed by graft polymerization, are known for a variety of specificpolymeric substrates. Still other surface modification techniquesutilize various methods including vapor deposition, plasma activation,sputtering, chemical etching, ion implantation, self-assembled monolayerdeposition etc. The feasibility of the specific method employed oftendepends upon both the substrate material as well as the specific surfacecharacteristics sought by the modification.

What is needed in the art is a method for modifying the surface of asubstrate that can be used on a wide variety of substrate materials. Inaddition, what is needed in the art is a method for modifying surfacesthat can be used to obtain a wide variety of modifications. For example,what is needed in the art is a surface modification process that can notonly be utilized for both organic and inorganic substrates, but can alsobe an efficient method for fixing a wide variety of functional materialsto the various substrates. For example, a method that can be utilized toattach biomolecules, such as proteins, low molecular weight substancesor polymeric substances to practically any substrate would be veryuseful in the art.

SUMMARY OF THE INVENTION

For purposes of this disclosure, the term ‘graft’ refers to a processwherein one material can be affixed to another material as hereindescribed. For instance, materials may be considered to be grafted toone another according to any process known in the art including, forexample, adsorption, absorption, bond formation (covalent, ionic, or anyother bond type), polymerization, or any other method suitable to affixone material to another from melt, gas phase, or liquid phase, asdesired.

In general, the present invention is directed to a process for modifyingthe surface characteristics of a substrate and the surface-modifiedsubstrates that can be formed according to the disclosed process.

In one embodiment, the process includes applying polymer comprisingmultiple epoxy groups and having a molecular weight of at least about2000 to the surface of a substrate. A portion of the epoxy groups on thepolymer can react at the surface binding the polymer to the surface atmultiple points along the polymer. For instance, in one embodiment, thepolymer can be covalently bound to the substrate surface at multiplepoints. In one embodiment, between about 5% and about 40% of the epoxygroups on the polymer can be utilized to bind the polymer to thesubstrate surface.

In addition, the polymer can be cross-linked to form a cross-linkedpolymeric anchoring layer bound to the substrate surface that containsadditional epoxy functionality throughout the layer. More specifically,the polymer can be cross-linked with itself as well as with otherpolymers or low molecular weight substances deposited on the surface. Inone embodiment, the polymer can be cross-linked at a portion of theepoxy groups on the polymer. For instance, between about 10% and about40% of the epoxy groups on the polymer can be utilized to cross-link thepolymer.

In one embodiment, the substrate can be heated to promote bonding andcross-linking of the epoxy-containing polymer. For instance, thesubstrate can be heated to a temperature of between about 70° C. andabout 130° C.

In certain embodiments, it may be preferred to oxidize the surface ofthe substrate prior to application of the epoxy-containing polymer, soas to promote the attachment of the polymer to the substrate surface.

Any high molecular weight polymer containing multiple epoxy groups canbe utilized in the disclosed process. For example, in variousembodiments, epoxidized polybutadiene, epoxidized polyisoprene, orpoly(glycidyl methacrylate) can be utilized to form the anchoring layer.

Similarly, the disclosed processes can be utilized with a vast number ofdifferent substrate types. For example, in certain embodiments, thedisclosed processes can be utilized to modify the surface of woven ornon-woven textile materials, natural or synthetic fibers, polymericmaterials, or inorganic materials.

The epoxy-containing polymer forming the anchoring layer can be appliedto the substrate surface according to any suitable process. For example,in one embodiment the polymer can be applied in a dip-coating process.In another embodiment, the polymer can be applied in a more controlleddeposition process, in order to, for example, apply the polymerheterogeneously across the surface of the substrate.

In one embodiment, the anchoring layer can be formed on the substratesurface to a depth of at least about 0.5 nanometers. For example, theanchoring layer can be between about 1 and about 10 nanometers on thesubstrate surface. In another embodiment, the anchoring layer can be atleast about 100 nanometers in depth on the substrate surface.

Following formation of the anchoring layer, additional material can begrafted to the substrate surface via the remaining epoxy functionalityin the anchoring layer. For example, in one embodiment, a polymerizationinitiator can be grafted to the anchoring layer, and a monomer may thenbe polymerized on the anchoring layer. For example, vinyl aromaticmonomers, acrylate monomers or methacrylate monomers can be polymerizedon the substrate surface. Optionally, a material can be directly graftedto the substrate at the remaining epoxy functionality. For example, apolymer or other macromolecule, such as a biomolecule, for example, canbe directly grafted to the substrate surface. In another embodiment, twoor more different materials can be grafted to the substrate surface atthe anchoring layer.

In one embodiment, the invention is directed to a ‘smart’ material thatcan be formed according to the disclosed processes. A smart material ofthe disclosed invention is one upon which two or more differentmaterials have been grafted to the anchoring layer, and the two or moredifferent materials can exhibit different responses to a known stimulus.For example, the two grafted materials can exhibit a different responsefrom one another when stimulated by contact of a known agent, thermalenergy, electromagnetic fields, or irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, to one of ordinary skill in the art, is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures, in which:

FIG. 1 is a representation of an epoxy-containing polymeric anchoringlayer bonded to a substrate surface;

FIG. 2 is a representation of one method for grafting functionalizedpolymers to an epoxy-containing anchoring layer on a substrate accordingto the present invention;

FIG. 3 describes one embodiment of a graft polymerization processaccording to the present invention;

FIGS. 4A, 4B, and 4C illustrate a hybrid polymer layer composed of twoimmiscible polymers grafted to an anchoring layer according to theprocess of the present invention;

FIGS. 5A, 5B, and 5C illustrate the wettability characteristics ofexemplary materials processed according to the processes of the presentinvention;

FIGS. 6A, 6B, and 6C are a series of scanning probe microscopy phaseimages obtained during a graft polymerization process according to thepresent invention;

FIG. 7 graphically illustrates the variation in thickness of a layer ofbromoacetic acid (BAA) affixed to a surface as a function of thethickness of an anchoring layer formed of poly(glycidyl methacrylate)(PGMA);

FIG. 8 illustrates the conversion of the anchoring layer epoxy groupsover time as a polymeric layer is deposited on a substrate surface viathe anchoring layer; and

FIG. 9 illustrates the thickness of a polystyrene (PS) brush grafted tothe surface of a substrate as a function of the thickness of aBAA-polymerization initiator layer.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachembodiment is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used in another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncover such modifications and variations as come within the scope of theappended claims and their equivalents.

The present invention is generally directed to a nearly universallyapplicable process for modification of a substrate surface and thesurface-modified substrates formed according to the disclosed processes.In particular, the surface modification processes of the presentinvention are suitable for almost any organic or inorganic substrate.

The present process generally includes the initial formation of anepoxy-containing polymeric layer on a surface. More specifically,according to the present invention, epoxy-containing polymers can bedeposited on a surface and can be cross-linked or otherwise stabilizedto form an epoxy-containing polymeric anchoring layer on the surface ofa substrate. While many of the epoxy groups on the anchoring layerpolymer can be utilized to firmly bind the polymers to the surface andto each other via cross-linking, a number of the epoxy groups can remainintact following formation of the anchoring layer. These remainingreactive epoxy groups can then be utilized for subsequent binding ofadditional materials to the surface of the substrate via the anchoringlayer. For example, functional molecules, biomolecules, low molecularweight substances or polymeric substances can be bound to the substratesurface via the anchoring layer.

The disclosed surface modification processes may be utilized in a widevariety of applications. A non-limiting list of exemplary applicationsfor surface modified products could include, for example, productsdisplaying increased hydrophilicity, hydrophobicity, dirt repellency,adhesiveness (such as for inks or dyes), flame retardance, lubrication,membrane selectivity, molecular recognition, colloidal stability,dispersivity and solvent resistance. In addition, improved bondingcapabilities of a surface in general may be attained through thedisclosed surface modification processes. For example, in oneembodiment, a specific bonding phase may be obtained by binding apartner of a specific binding pair to a surface. This modified surfacecan then be used in, for example, identification or filteringapplications. In another embodiment, a surface, for example a metallicsurface, may be modified to display increased corrosion resistance.Wettability characteristics of fibers and textile materials may beimproved through surface modification so as to improve sizing, finishingand dyeing of the materials in addition to improved grease repellency,permanent press properties, and quickness of drying of the finalproducts.

There are countless medical and biological applications for surfacemodified materials. For example, materials inserted into blood vessels,body cavities, eyes, etc. could be modified so as to be morehydrophilic, in order to increase lubricity or wettability of thematerials. In some instances, it may be advantageous for surfaces ofmedical devices to have the capability to serve as a temporary orpermanent depot for biomaterials such as various physiologically orpharmacologically active agents, such as antibacterial agents, forexample. In addition, surfaces of biological materials can be modifiedso as to prevent thrombosis, or blood clotting at the surface followinginsertion.

Generally, any organic or inorganic material may be modified at asurface according to the present invention. In addition, though certainsubstrates, for example certain organic substrates, may require apre-treatment process, most materials will already comprise suitablefunctionality at the surface to be processed according to the presentlydisclosed invention with no pre-treatment necessary. A non-exhaustivelist of possible materials suitable for modification according to theprocesses of the present invention can include, for example, variousfiber and textile materials, including natural and synthetic fibrousmaterials; polymeric materials, including polyolefins such aspolyethylene and polypropylene based materials, including ultra highmolecular weight polyethylene, polyethylene terephthalate (PET), siliconresins, and nylons; and inorganic materials including silicon, glass,and metal substrates such as titanium, alumina, gold, silver, and alloymaterials. Moreover, when considering fibrous materials, the fibrousmaterial itself may be treated according to the present invention.Alternatively, individual fibers may be treated according to the presentinvention prior to formation of a woven or nonwoven material.

According to the present invention, a polymeric anchoring layer can bedeposited on a substrate surface. While the polymers used to form theanchoring layer can comprise multiple different functionalities, theywill always include multiple epoxy functionality. Epoxy is highlyreactive under a wide variety of conditions. For instance, epoxy canreact with any of carboxy, hydroxy, amino, thiol, or anhydridefunctional groups under a wide variety of conditions. As such, theepoxy-containing polymers of the present invention can be readily boundto surfaces via functionalities already available on most substrates. Inother words, preprocessing of a substrate prior to deposition andformation of the anchoring layer will not be required in manyembodiments of the present invention. In addition, the particular bondformed between the substrate and the epoxy groups on the polymer candepend upon the functionality on the substrate and as such, the polymermay be bound via covalent bonds, hydrogen bonds, ionic bonds, or anyother strong or weak bond, as desired.

Beneficially, the epoxy-containing polymers deposited on the surface cancross-link following or even during initial deposition. As such, thedeposited epoxy-containing polymers can form a permanent orquasi-permanent layer on the substrate. Moreover, the polymers utilizedto form the anchoring layer will include multiple epoxy functionality.Due to the multiple epoxy groups available on the polymers, theepoxy-containing polymers that form the anchoring layer of the presentinvention can form a consolidated, cross-linked anchoring layer that isfirmly affixed to the substrate surface and still have large levels ofadditional reactive epoxy functionality remaining in the networkfollowing formation of the layer. This remaining epoxy functionality canprovide a relatively simple route for subsequent surface modification ofthe substrate by the further reaction of the anchoring layer withadditional materials to provide the desired surface characteristics onthe substrate.

In general, epoxy-containing polymers suitable for the processes of thepresent invention include high molecular weight epoxy-containingpolymers having a plurality of epoxy sites. For example, in oneembodiment, an epoxy-containing polymer having a molecular weight of atleast about 2,000 may be used to form the anchoring layer. In oneembodiment, an epoxy-containing polymer having a molecular weight overabout 100,000 may be utilized to form the anchoring layer on thesubstrate surface. In any case, the number of epoxy groups on thepolymer will be at least 3 times higher than those in an epoxy resin.For purposes of this disclosure, epoxy resins are herein defined aslow-molecular-weight pre-polymers or oligomers with typically from twoto six epoxide groups per molecule

Beneficially, there are a wide variety of epoxy-containing polymersalready available in the art that can be utilized in the disclosedprocesses. As such, in one embodiment, an anchoring layer can be formedon a substrate surface with readily available materials according to theprocesses of the present invention. Optionally, the epoxy-containingpolymers may be pre-functionalized or otherwise preprocessed accordingto any desired methodology as is known in the art to provide a specificepoxy-containing polymer for formation of the disclosed anchoring layer.For instance, in certain embodiments, the epoxy-containing polymerutilized to form the anchoring layer according to the present inventioncan include backbone material or side chain functionality so as tointeract in a specific way with the substrate material or with materialsthat can be subsequently grafted to the anchoring layer. For example, incertain embodiments, an epoxy-containing polymer may be utilized whichis miscible with the material to be subsequently grafted to theanchoring layer. In other instances, it may be preferable to utilize anepoxy-containing polymer which is immiscible with the subsequentlygrafted material.

In one embodiment, the epoxy-containing polymer can include one or moreadditional functionalities or moieties which can provide desiredcharacteristics to the modified surfaces. Additionally, theepoxy-containing polymer can include additional functionalities ormoieties that can be utilized in affixing additional materials to thesubstrate surface via specific or non-specific interactions with theanchoring layer. While not intending to be in any way a limiting list,exemplary moieties may include various hydrophobic or hydrophilicmoieties as are generally known in the art including pyridine, tertiaryamines, double bonds, chelates, protected amino, hydroxyl, thiol, andcarboxyl functional groups.

In one embodiment, the epoxy-containing polymer that can form theanchoring layer can be epoxidized polybutadiene. In another embodiment,epoxidized polyisoprene can form the anchoring layer on the substratesurface. In another embodiment, poly(glycidyl methacrylate) (PGMA) canbe used to form the anchoring layer. Generally, any epoxy-containinghomopolymer or copolymer possessing about 10 or more oxyrane rings perpolymer can be utilized for the anchoring layer formation. In otherembodiments, the polymer can include greater epoxy functionality. Forexample, in one embodiment, the polymer can include one or more epoxygroups on each repeating unit of the polymer. In another embodiment, thepolymer can be a block, graft, alternating, or random copolymer, inwhich at least one of the monomers found in the copolymer includes oneor more epoxy functionalities on each monomer unit, while the othermonomer(s) carry no epoxy functionality.

By utilizing a high molecular weight epoxy-containing polymer, it hasbeen discovered that a large amount of the epoxy-containing material maybe attached to the substrate surface in the anchoring layer thus formed.For example, by forming an anchoring layer of cross-linked PGMA withmolecular weight of 24,000 g/mol on a silicon wafer substrate, theamount of material grafted to the anchoring layer can be from about 2 toabout 4 times greater than the amount of polymeric material attached tothe surface when a low molecular weight epoxy-containing substance witha single epoxy functionality, for example, epoxysilane((3-glycidoxypropyl)trimethoxysilane) is utilized, which generallyattains a graft density at maximum of about 0.3 chains/nm². In general,the high molecular weight epoxy-containing polymers of the disclosedinvention can be grafted at a graft density greater than about 0.3chains/nm². For example, between about 0.5 and about 1 chains/nm². Inone embodiment, the polymer can be grafted at a grafting density ofabout 0.8 chains/nm².

The epoxy-containing polymer of the disclosed anchoring layer may beapplied to the substrate surface according to any suitable methodology.For example, in one embodiment, a polymer solution may be formed and thesubstrate may be sprayed with or immersed in the polymer solution. Inone embodiment, a fairly dilute solution of the polymer may be formed,and the substrate may be dip-coated in the solution. For example, asolution may be formed containing from about 0.02% to about 0.5% of thepolymer by weight in an organic solvent and the substrate may bedip-coated in the solution. In other embodiments, however, less dilutesolutions of the polymer may be utilized.

When utilizing a formation method such as that described above, anysuitable solvent may be used to form an epoxy-containing polymersolution. Generally, the solvent may be an organic solvent, such as, forexample, tetrahydrofuran (THF) or a ketone-based solvent such asmethyl-ethyl ketone. Optionally, aqueous or aqueous/alcoholic solutionsare not outside the scope of the present invention, though anaqueous-based solution may present certain difficulties due to thetendency of the epoxy groups to hydrolyze in the presence of water. Forinstance, in certain embodiments, it may be preferable to utilize thepolymer solution fairly soon after formation, with little storage timeprior to use.

Generally, most surfaces will already contain suitable reactivity suchthat the epoxy-containing polymer may be bound to the surface with nopretreatment of the surface necessary. However, certain unreactivesubstrate surfaces may require pretreatment prior to formation of theanchoring layer on the surface. For example, some polymeric surfacessuch as poly(ethylene terephthalate), polyethylene, and polypropylenesurfaces may require functionalization such as oxidation of the surfaceprior to contact with the epoxy-containing polymer and formation of theanchoring layer on the substrate.

In those instances wherein pre-functionalization of the substratesurface is desired, functionalization may be obtained according to anysuitable method. For example, the surface of an organic substrate may beoxidized through any suitable oxidation method including, but notlimited to, corona discharge, chemical oxidation, flame treatment,plasma treatment, or UV radiation.

When the substrate is contacted with the epoxy-containing polymer, afraction of the epoxy groups on the polymer can react with functionalgroups on the substrate surface and bind the epoxy-containing polymer tothe surface. The attachment may involve a chemisorption or aphysisorption of the polymer on the substrate surface, depending uponthe materials involved. For example, in certain embodiments, it isbelieved that hydrogen bonds can form by reaction between functionalgroups on the surface of the substrate and epoxy groups on the polymer.In other embodiments, however, it is believed that covalent bonds canform between functional groups on the surface of the substrate and theepoxy groups on the polymer. More specifically, in certain embodiments,following attachment, the anchoring layer has been shown to remainfirmly affixed to the substrate surface following vigorous solventtreatment such as solvent treatment with Dimethylformamid (DMF),Dimethyl sulfoxide (DMSO), tetrahydrofurane (THF), toluene, or methylethyl ketone, suggesting that the epoxy-containing polymer may bechemically bonded to the surface. Optionally, a less permanentattachment can be formed between the anchoring layer and the substratesurface, making the anchoring layer a temporary layer, such as in thoseembodiments wherein the desired surface modification is not meant to bea permanent feature of the substrate.

FIG. 1 illustrates one embodiment of an anchoring layer generally 30according to the present invention. As can be seen in FIG. 1, a singleepoxy-containing polymer can be grafted to the surface 14 of thesubstrate 12 at multiple points 10 along the length of the polymer whereepoxy groups 16 of the polymer have reacted with functionalities on thesurface 14 of the substrate 12. In this manner, a secure attachment canbe formed between the epoxy-containing polymer and the substrate surface14. In addition, as the epoxy-containing polymer can be attached to thesubstrate surface at multiple random points 10 along the length of thepolymer, the individual polymer can form trains 20, tails 22, and loops24 that can extend the height of the polymer above the substrate surfaceproviding a depth to the anchoring layer 30, as can be seen in FIG. 1.

The epoxy-containing polymers applied to the surface of the substratethat form the anchoring layer of the present invention include excessquantities of epoxy functionality on the polymer in addition to thoseused for attachment of the polymer to the substrate surface. As such, inaddition to binding the polymer to the substrate surface, the epoxyfunctionality on the polymer can cross-link the polymers. For instance,as can be see in FIG. 1, the polymer can form cross-links 32 toself-cross-link a single polymer as well as to cross-link adjacentpolymers to each other. The epoxy-containing polymers applied to thesubstrate can thus form a permanent or quasi-permanent anchoring layeron the substrate.

In one embodiment, the polymers can spontaneously cross-linksimultaneous with the attachment reactions as the polymers are bound tothe surface. In another embodiment, the epoxy-containing polymers may beencouraged to cross-link through addition of energy, such as thermal orradiant energy. In yet another alternative embodiment, theepoxy-containing polymers can cross-link during subsequent graftingprocesses. Additionally, combinations of cross-linking protocols maytake place. In any case, according to the presently disclosed process, across-linked epoxy-containing polymeric network can be formed on atleast a portion of the substrate surface creating an anchoring layer onat least that portion of the surface.

For example, in one embodiment, the polymers can cross-link. Accordingto one possible self-cross linking protocol, attachment of theepoxy-containing polymer to the surface through epoxy ring opening cangenerate hydroxyl groups in the glycidyl fragment. In addition, minoroccurrence of opened epoxy rings can be present on the polymer due totraces of water in the environment. At some point, such as during anannealing process, for example, these hydroxyl groups can react withanother epoxy ring yielding a cross-link having an ether linkage and canalso generate a new hydroxyl group in the polymer that is able toinitiate further cross-linking. Moreover, in one embodiment, across-linking agent can be included with the polymer solution to furtherencourage cross-linking of the polymer. In general, a cross-linkingagent can be any compound bearing two or more moieties able to reactwith epoxy ring. For example, ethylene diamine, hydrazine, dicarboxylicacids and the like can be utilized.

In some embodiments, heat may be added to the system in order to speedup the anchoring layer forming reactions on the substrate surface. Forexample, in one embodiment, the rates of both the cross-linkingreactions and the substrate attachment reactions can be increased byheating the substrate before, during, or after contact with theepoxy-containing polymer to a temperature of between about 40° C. andabout 150° C. In one embodiment, following the coating process, thesubstrate can then be heated and held for about 5 minutes at atemperature of about 100° C. to promote both the attachment andcross-linking reactions that can form the anchoring layer on thesubstrate surface.

Following attachment and cross-linking of the epoxy-containing polymeron the surface of a substrate, the polymeric anchoring layer can stillinclude an amount of reactive epoxy that can be utilized for attachmentof additional materials to the anchoring layer. For example, in oneembodiment of the present invention, between about 10% and about 30% ofthe epoxy groups on an epoxy-containing polymer can react with surfacefunctionalities and form attachment points between the polymer and thesubstrate surface. In addition, between about 10% and about 40% of theepoxy groups on the polymer can be utilized in cross-linking the layer.The remaining epoxy groups on the epoxy-containing layer, between about20% and about 50% in some embodiments, can still remain within theanchoring layer following formation of the cross-linked anchoring layeron the substrate surface and can be available for subsequent attachmentof additional materials to the surface of the substrate.

Beneficially, the thickness of the anchoring layer and, consequently,the amount of epoxy functionality remaining on the substrate surfacefollowing formation of the anchoring layer, may be controlled accordingto the presently disclosed process by varying process conditions. Forexample, in one embodiment, the thickness of the anchoring layer may bemodified by varying the solvent employed and/or the concentration of theepoxy-containing polymer solution during deposition. In one embodiment,the thickness of the anchoring layer can depend on the planarity of thesubstrate surface. By varying process conditions of the deposition, apredetermined and wide variety of anchoring layer thickness can beformed. For example, in certain embodiments, an epoxy-containinganchoring layer may be formed on a substrate surface of up to or evengreater than about 100 nm. In one embodiment, an anchoring layer with athickness of at least about 0.5 nm may be formed according to thedisclosed process. In another embodiment, an anchoring layer with athickness from about 1 nm to about 10 nm may be formed according to thedisclosed process.

The anchoring layer formed according to the processes of the presentinvention can be smooth and, in one embodiment, can uniformly cover thesurface of a substrate. For instance, in one embodiment the anchoringlayer can cover the entire surface of a substrate, for example when adip-coating application method is used to form the layer. Alternatively,the anchoring layer may cover only a portion of a substrate surface. Forexample, in certain embodiments of the present invention, the anchoringlayer may be heterogeneous across the substrate surface such as in apattern, such that only a portion of the surface includes the anchoringlayer. Heterogeneous coverage of the substrate surface can, in oneembodiment, be attained by more controlled methods of deposition forapplying the epoxy-containing polymer to the substrate, such as sprayingor printing processes, for example.

Following formation of an anchoring layer on a substrate surfaceaccording to the processes herein described, additional materials may begrafted to the substrate surface by reaction with the epoxyfunctionality still remaining in the anchoring layer. For instance, inone embodiment, functionalized polymers or macromolecules such asbiomolecules (proteins, DNA, or polysaccharides), polyethylene glycol,polyacrylates, polymethacrylates, poly(vinyl pyridine), polyacrylamide,or polystyrene may be directly grafted to the epoxy-containing anchoringlayer.

In general, it has been found that the thickness of the formed anchoringlayer can have little or no decisive influence on the amount of materialthat can be subsequently grafted to the substrate surface in thoseembodiments wherein the materials to be grafted to the substrate surfaceare immiscible with the epoxy-containing polymer. However, in thoseembodiments wherein materials are to be grafted that are miscible withthe epoxy-containing polymer, the grafted amount can be stronglydependent on the anchoring layer thickness. This is believed to be dueto the ability of a miscible material to penetrate the depth of theanchoring layer and react with available epoxy throughout the layer,allowing material to be grafted throughout the layer, and not just onthe surface of the layer, as would be the case for an immisciblematerial.

In one embodiment, materials may be grafted to the anchoring layer bydirect reaction between the material and the epoxy functionalityremaining on the substrate surface following formation of the anchoringlayer. FIG. 2 illustrates one embodiment of the present invention inwhich a macromolecule 204 possessing any of several different possiblefunctional groups 206, e.g., carboxy, anhydride, amino and/or hydroxygroups, may be directly grafted to the epoxy-containing anchoring layer30 on the surface of a substrate 12. In this embodiment, themacromolecule 204 can be attached to the anchoring layer 30 at thosefunctional groups 206 where the macromolecule 204 can react with freeepoxy groups 16 in the anchoring layer 30. For example, in variousembodiments, hydrophobic and hydrophilic homopolymers (polyethyleneglycol, polyacrylates, polkymethacrylates, poly(vinyl pyridine),polyacrylamide or polystyrene), random, graft, or block copolymers maybe attached to the substrate surface via direct attachment to theanchoring layer.

In another embodiment illustrated in FIGS. 3A–3C, a grafted material maybe ‘grown’ on the anchoring layer such as through a graft polymerizationprocess. In this embodiment, a graft polymerization initiator 32 can begrafted to the anchoring layer 30 at epoxy groups 16 as shown in FIG.3B. Subsequent contact between the substrate 12 carrying thepolymerization initiator 32 and monomer M at reaction conditions canlead to the polymerization of the monomer M on the substrate surface viathe anchoring layer 30 as shown at FIG. 3C. In general, thepolymerization initiating groups can be grafted to the anchoring layervia covalent bond-forming reactions with the epoxy groups, though thisis not a requirement of the present invention.

Though not wishing to be bound by any particular theory, it is believedthat the unique three dimensional network of the anchoring layer of thepresent invention including reactive epoxy throughout the layer canallow for very large amounts of material to be grafted to the surface ofa substrate. For example, when considering a graft polymerizationprocess such as that described above, it is believed that large amountsof individual polymerization initiator molecules can penetrate thecross-linked network of the anchoring layer easily to reach reactiveepoxy groups across the entire depth of the anchoring layer. Inaddition, monomer molecules can also penetrate the cross-linked networkof the anchoring layer to reach the polymerization initiators graftedwithin the anchoring layer. Therefore, polymerization can occur not juston the surface of the anchoring layer, but throughout the entire depthof the anchoring layer as well, and significantly larger amounts ofpolymeric material up to about 1000 mg/m² in one embodiment may begrafted on the substrate surface.

According to one embodiment of the present invention, a polymerizationinitiator for an Atom Transfer Radical Polymerization (ATRP), as isgenerally known in the art, may be grafted to the anchoring layer.Following or concurrent with attachment of the initiator, the substratecan be contacted with monomer, and polymerization can be initiated fromthe substrate surface via the anchoring layer. Thus, a polymeric layerpossessing high grafting density, for example up to about 2 chains/nm²in one embodiment, may be synthesized on the substrate surface via theanchoring layer.

Various polymerization initiators may be utilized in a graftpolymerization modification process according to the present invention.In one embodiment, an acid may be used such as, for example, bromoaceticacid, which can be grafted to the free epoxy groups of the anchoringlayer at the carboxylic functionality. Other polymerization initiatorsmay be alternatively utilized, however. For instance, any polymerizationinitiator displaying carboxy, anhydride, amino, or hydroxy functionalitythat may graft to the epoxy-containing anchoring layer may be utilized.Monomers which may be polymerized on the surface of the substrate fromthe polymerization initiator are generally well known in the art andinclude, for example, vinyl aromatic compounds including, for example,styrene and 2-vinylpyridine, acrylates, or methacrylates can bepolymerized. In general, any vinyl monomer that may polymerize byradical polymerization employing the initiator according to any knownpolymerization process as is generally known in the art may be utilized.

In one embodiment of the present invention, the substrate can be graftedwith two or more different materials at the anchoring layer to form ahybrid material. For example, the substrate, following formation of theanchoring layer, can be contacted with two or more different materials,either at the same time or in a step-by-step process, as desired, suchthat the materials may be either directly grafted or polymerized ontothe epoxy-containing anchoring layer. For example, one material may bedirectly grafted and another material may be grafted through apolymerization process. Alternatively, all of the grafted materials maybe grafted through the same process, i.e., direct grafting of thematerials or graft polymerization. For example, in one embodiment, afirst initiating system may be attached at some of the epoxy groups,followed by a graft polymerization process. Then, a second initiatingsystem may be attached to the remaining epoxy sites on the substratesurface and a second graft polymerization reaction may be carried out.

In one embodiment, hybrid materials can be formed according to theinvention wherein the graft area for each different material can becontrolled. Alternatively, a hybrid material can be formed with all ofthe different grafted materials spread across the substrate in a mixedfashion. For instance, in one embodiment, a first material can begrafted to a portion of the substrate surface, while the rest of thesurface is prevented from reacting with the first material, such as witha mask. Following grafting of the first material, a second material canthen be applied to the previously masked areas. In another embodiment,the substrate surface carrying the disclosed anchoring layer can becontacted with two or more materials at one time, and all of the graftedmaterials may be located across the entire anchoring layer, in a mixedfashion.

According to one particular embodiment of the present invention, ahybrid material including two or more different materials grafted to asubstrate surface via the disclosed anchoring layer can be formed toproduce a ‘smart’ material.

‘Smart’ materials are herein defined to be materials possessing theability to switch and/or display varying properties by application ofvariation in external stimuli. For example, one embodiment of a smartmaterial of the present invention is a binary (hybrid) polymeric graftedlayer composed of two immiscible polymers as can be seen in FIG. 4. Inthis embodiment, two different polymers 42, 44 have been grafted tosubstrate 12 via anchoring layer 30. Due to phase segregation, themorphology of the mixed polymer layer 40 can be sensitive to thesurrounding medium. For instance, the hybrid layer 40 can be switchedbetween different surface energetic states illustrated at FIGS. 4B and4C upon exposure to different stimuli such as different solvents,different field energies, and the like. The differentiating stimuli canbe of any type, including radiant, mechanical, thermal, electrical,magnetic, or chemical stimulation. The interaction of the binary polymerlayer with changing external stimulation can cause a change of thesurface properties of the polymer film due to the differing response ofthe grafted materials 44, 42 to the stimulation. For example, a hybridsurface layer 40 can be switched between different states, e.g.demonstrating different levels of hydrophilicity, adhesion,conductivity, or interaction with some substance depending upon theconditions of the substrate and the variation in response to thoseconditions of the different materials forming the hybrid layer 40.Moreover, hybrid layers of the present invention are not limited tobinary systems. Multiple materials may be grafted to the substratesurface according to the processes of the present invention.

Reference now will be made to various embodiments of the invention, oneor more examples of which are set forth below. Each example is providedby way of explanation of the invention, not as a limitation of theinvention. In fact, it will be apparent to those skilled in the art thatvarious modifications and variations may be made of this inventionwithout departing from the scope or spirit of the invention.

EXAMPLE 1

The process of the present invention was utilized for direct attachmentof polymers to polymeric surfaces. Hydrophilic poly(ethylene glycol)(PEG) and hydrophobic polystyrene (PS) polymers were directly grafted topolyethylene terephthalate (PET), polyethylene, and polysiloxanesubstrates via an epoxy-containing PGMA anchoring layer.

Initially, the polymeric substrates were plasma treated for short time.The plasma treated surfaces were then dip coated with PGMA (M_(n)=24,000g/mol) from 0.05% solution in MEK (methyl ethyl ketone). The epoxymodified substrates were then grafted with carboxy end-functionalized PSand PEG at 130° C. and 70° C. respectively, in a vacuum oven. Theunbound polymer was removed by multiple washing with toluene, includingwashing in an ultrasonic bath.

FIG. 5A illustrates the morphology and wettability of a PET surfacemodified with a PS layer. FIG. 5B illustrates the morphology andwettability of a PET surface modified with a PEG layer. The scanningprobe microscopy images (1×1 μm), a portion of which is illustrated inFIGS. 5A and 5B, show that the polymeric surfaces were completelycovered with the grafted layers. The polymer graft dictated the surfaceproperties of the polymer film. The synthesized layers could not beremoved by multiple rinsing in hot solvents including such strongsolvent as DMF (Dimethylformamid). The obtained results show thatpolymers possessing functional groups may be grafted to polymericsurfaces modified with a PGMA anchoring layer.

PEG and PS were also successfully grafted to polyester fiber and textilematerials utilizing the processes of the present invention according tothe above-described process. FIG. 5C illustrates a droplet of water onthe surface of a polyester textile material modified with a graftedpolystyrene layer via an epoxy-containing PGMA anchoring layer.

EXAMPLE 2

In this example, polymerization was initiated on a silicon wafer surfacecontaining an anchoring layer of the present invention. FIG. 3illustrates the process of the example. As shown in FIG. 3 a, ananchoring layer 30 of PGMA with epoxy functionality was deposited on thesurface of the substrate 12, a silicon wafer. Bromoacetic acid (BAA) wasused as an initiator 32 of Atom Transfer Radical Polymerization (ATRP).The BAA initiator was attached to the PGMA anchoring layer from gasphase through the reaction between carboxylic and epoxy functionalities.The deposition was performed at a variety of different temperatures aswas the subsequent polymerization process. Temperatures ranged for bothprocesses from about 30° C. to about 115° C.

In various runs, carried out over 24 hours at 80° C., the PGMA layerthickness was varied, which allowed control over the amount of BAAinitiator attached to the surface. FIG. 7 graphically illustrates thethickness of the BAA layer obtained as a function of the thickness ofthe anchoring PGMA layer. As can be seen, there was a nearly linearcorrelation between the quantity of the epoxy polymer attached to thesurface and amount of the initiator grafted. Moreover, kinetics of theBAA initiator deposition process were also found to be suitable forregulation of the BAA amount reacted with the primary PGMA anchoringlayer. As such, it was possible to regulate not only the amount of BAAdeposited on the substrate but also numbers of remaining epoxy groupsfollowing formation of the PGMA/BAA layer.

During attachment of BAA initiator, two competitive reactions may occur:(a) reaction between a carboxy group of BAA and an epoxy group of PGMAand (b) self-cross-linking of the PGMA layer owing to the highconcentration of epoxy groups. The second reaction may decrease thesurface concentration of the epoxy groups available for other reactions.FIG. 8 graphically illustrates the conversion of the PGMA epoxy groupsas a function of time during BAA deposition at 90° C.

Further, to study the extent of the potential deactivation of availableepoxy, dodecyl amine (DA) was grafted to PGMA films annealed at 120° C.for different periods of time to induce cross-linking of the PGMA film.This low molecular weight substance was used as a probe for the presenceof accessible epoxy groups. The amine attachment was carried out in warm(40° C.) toluene solution for 8 hours. Data obtained showed thatapproximately 40% of epoxy groups were still available on the surface ofthe PGMA film after 4 hours of annealing and that the drop in initialactivity of the PGMA film due to annealing occurred almost immediatelywhen the film was heated.

Upon reaction between the PGMA anchoring layer and the BAApolymerization initiator, the silicon wafer became coated with a layerof the PGMA/BAA macroinitiator at a surface. The layer was found to besmooth, homogeneous and uniformly covered the surface of the wafer.

Following formation of the PGMA/BAA macroinitiator layer, the surface ofthe wafer was further modified via ATRP of styrene. As a result of thepolymerization, a polystyrene layer was firmly grafted to the surface ofthe wafer. FIG. 9 graphically illustrates the thickness of thepolystyrene brush obtained via graft polymerization as a function of thethickness of the BAA layer applied to the wafer. The ATRP reactionsillustrated in FIG. 9 were carried out at 115° C. for 8 hours.

The same polymerization process was also utilized for polymerization ofa polystyrene layer on a polymeric substrate. FIG. 6 shows SPM imagesand values of water contact angles for virgin PET surface (FIG. 6 a),PET surface covered with PGMA/BAA combination (FIG. 6 b), and thegrafted polystyrene layer (FIG. 6 c). One can see that the surfacemorphology of the PET film was changed after the polymerization.

EXAMPLE 3

Hybrid polymer layers of varying composition including graftedpolystyrene (PS) and poly(2-vinylpyridine) (PVP) were formed on a PETtextile material. The layers were synthesized by grafting the polymersto an epoxy-containing anchoring layer which had been formed accordingto the process of Example 1, above. FIG. 4 is a representation of theprocess.

Using PGMA as an anchoring layer, a switchable polymer nanolayer wasformed on the surface of a polyester textile material includingpolystyrene and poly(2-vinylpyridine). It was found that the surfaceproperties of the PET fabric changed after being treated with differentsolvents. When the fabric was exposed to toluene, the polystyrene chainspreferentially occupied the surface of the substrate, thus, thesubstrate surface became hydrophobic and upon subsequent contact withwater, the water did not penetrate through the material. Conversely,when the fabric was exposed to ethanol, the PVP chains preferentiallyoccupied the surface of the substrate, and upon subsequent contact withwater, the water did penetrate throughout the PET textile material.

It will be appreciated that the foregoing examples, given for purposesof illustration, are not to be construed as limiting the scope of thisinvention. Although only a few exemplary embodiments of this inventionhave been described in detail above, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention which isdefined in the following claims and all equivalents thereto. Further, itis recognized that many embodiments may be conceived that do not achieveall of the advantages of some embodiments, yet the absence of aparticular advantage shall not be construed to necessarily mean thatsuch an embodiment is outside the scope of the present invention.

1. A process for modifying the surface characteristics of a substratecomprising: applying a polymer comprising multiple epoxy groups andhaving a number average molecular weight of about 2000 or greater to asubstrate surface, wherein the substrate is formed of a substratematerial that comprises functional groups that are reactive with epoxy;reacting only a portion of the epoxy groups on the polymer with at leasta portion of the functional groups of the substrate material to bind thepolymer directly to the substrate material at multiple points along thepolymer; and cross-linking the polymer via reaction of only a portion ofthe epoxy groups on the polymer to form a cross-linked polymericanchoring layer bound directly to the substrate material at thesubstrate surface, wherein the anchoring layer comprises epoxyfunctionality.
 2. The process of claim 1, further comprising grafting atleast one material to the anchoring layer at the epoxy functionality. 3.The process of claim 2, wherein the at least one material comprises apolymerization initiator.
 4. The process of claim 3, further comprisingpolymerizing a monomer on the anchoring layer at the polymerizationinitiator.
 5. The process of claim 4, wherein the monomer is capable ofradical polymerization.
 6. The process of claim 4, wherein the monomeris selected from the group consisting of a vinyl aromatic, an acrylate,and a methacrylate.
 7. The process of claim 2, wherein the at least onematerial comprises a polymer, a macromolecule, or a biomolecule.
 8. Theprocess of claim 1, wherein the polymer is applied to the substratesurface in a dip-coating process.
 9. The process of claim 1, wherein thepolymer is applied to the substrate surface heterogeneously.
 10. Theprocess of claim 1, further comprising grafting two or more materials tothe anchoring layer.
 11. The process of claim 1, further comprisingheating the substrate to a temperature of between about 40° C. and 150°C. following application of the polymer to the substrate surface. 12.The process of claim 1, wherein the substrate is heated subsequent toapplication of the polymer comprising multiple epoxy groups to thesubstrate surface.
 13. The process of claim 1, further comprisingoxidizing the substrate surface prior to application of the polymer tothe substrate surface.
 14. The process of claim 1, wherein the polymeris selected from the group consisting of epoxidized polybutadiene,epoxidized polyisoprene, and epoxidized poly(glycidyl methacrylate). 15.The process of claim 1, wherein the polymer is covalently bound to thesubstrate material at multiple points along the polymer.
 16. The processof claim 1, wherein the substrate material is a textile material, afiber, a polymeric material, or an inorganic material.
 17. A process formodifying the surface characteristics of a substrate comprising:applying a polymer comprising multiple epoxy groups and having a numberaverage molecular weight of about 2000 or greater to a substratesurface, wherein the substrate is formed of a substrate material thatcomprises functional groups that are reactive with epoxy; reactingbetween about 5% and about 40% of the epoxy groups on the polymer withat least a portion of the functional groups of the substrate material tobind the epoxy-containing polymer directly to the substrate material atmultiple points along the polymer; reacting between about 20% and about30% of the epoxy groups on the polymer to form cross-links such that across-linked polymeric anchoring layer is formed bound directly to thesubstrate material, wherein the anchoring layer comprises epoxyfunctionality; and grafting at least one material to the anchoring layerat the epoxy functionality.
 18. The process of claim 17, wherein the atleast one material comprises a polymerization initiator.
 19. The processof claim 18, further comprising polymerizing a monomer on the anchoringlayer at the polymerization initiator via an atom transfer radicalpolymerization.
 20. The process of claim 19, wherein the monomer isselected from the group consisting of a vinyl aromatic monomer, anacrylate, and a methacrylate.
 21. The process of claim 17, wherein theat least one material comprises a polymer, a macromolecule, or abiomolecule.
 22. The process of claim 17, wherein the epoxy-containingpolymer is applied to the substrate surface in a dip-coating process.23. The process of claim 17, wherein the epoxy-containing polymer isapplied to the substrate surface heterogeneously.
 24. The process ofclaim 17, further comprising grafting two or more materials to theanchoring layer.
 25. The process of claim 17, further comprisingoxidizing the substrate surface prior to application of theepoxy-containing polymer to the substrate surface.
 26. The process ofclaim 17, wherein the epoxy-containing polymer is selected from thegroup consisting of epoxidized polybutadiene, epoxidized polyisoprene,and epoxid ized poly(glycidyl methacrylate).
 27. The process of claim17, wherein the epoxy-containing polymer is poly(glycidyl methacrylate)comprising epoxy functionality.